FIG. 1 is a simplified block diagram of a related art radar transceiver 10. A magnetic circulator 12 is coupled between a transmit (TX) port 14, a receive (RX) port 16, and an antenna port 18. The magnetic circulator 12 directs a TX signal and an RX signal to and from an antenna 20 coupled to the antenna port 18. A limiter 22 coupled between the magnetic circulator 12 and the RX port 16 is included to protect a low noise amplifier (LNA) 24 from potentially damaging RF signal levels of a harmful RX signal such as a jammer signal. For the purpose of this disclosure, a TX signal is defined as a provided signal that is desired to be transmitted through the antenna port 18 to a load such as the antenna 20. Also for the purpose of this disclosure, a jammer signal is defined as a received signal that is not desired to be passed to the RX port 16.
In a TX mode, the TX signal is amplified to a relatively high power level by a power amplifier (PA) 26 and passed to the magnetic circulator 12 through the TX port 14. The amplified TX signal would ideally be 100% directed to the antenna 20 from which the amplified radar signal is radiated toward a radar target (not shown). When in an RX mode, a radar signal reflected from the radar target is received by the antenna 20. Ideally, the relatively weak radar signal is 100% directed to the LNA 24 for amplification before detection and processing.
The magnetic circulator 12 performs a signal routing function. However, the magnetic circulator 12 is not ideal and thus only provides finite isolation. In other words, the magnetic circulator 12 does not direct 100% of the TX signal as intended, therefore, some TX power will leak into an RX path made up of the limiter 22, the RX port 16 and the LNA 24. Also, if the antenna 20 gets illuminated by another high power source such as a jamming signal, high power levels would be directed to the LNA 24. Therefore, to protect the LNA 24 from either scenario, the limiter 22 is typically included in front of the LNA 24 in the RX path to limit the voltage amplitude of the jamming signal before the jamming signal passes through the RX port 16 to the LNA 24. Typically, the limiter 22 is a p-type-intrinsic-n-type (PIN) diode based circuit.
Modern realizations of both the limiter 22 and the magnetic circulator 12 are bulky and expensive. Moreover, the magnetic circulator 12 is typically the largest component integrated within a radar transceiver module (not shown). A further undesirable characteristic is that the magnetic circulator 12 and the limiter 22 are not generally compatible with monolithic implementation utilizing gallium arsenide (GaAs) or gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) technology. These undesirable issues significantly impact any feasibility of a fully integrated radar transceiver frontend. What is needed is a monolithically compatible circuit that replaces the magnetic circulator 12 and the limiter 22 in radar frontends.